Lyotropic liquid crystals represent the oldest type of the fourth state of matter, which combines the properties of crystalline solids and normal liquids, and is therefore referred to as a mesophase. Despite their diverse applications in medicine, pharmacy, and cosmetics, they still play a secondary role compared to competing thermotropic mesophases. The aim of this book is to introduce chemists, physicists, and pharmacists, as well as advanced students, to the fundamentals of lyotropic liquid crystals, to highlight their similarities and differences with thermotropic liquid crystals, and to demonstrate the various possibilities of their application.